Method for mitigating inter cell interference and device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method and a device therefor, wherein the method comprises the steps of: receiving a PDCCH signal that contains scheduling information from a base station on a first subframe; receiving a PDSCH signal corresponding to said PDCCH signal from said base station on a second subframe; and decoding said PDSCH signal, wherein an interval between said first subframe and said second subframe is varied.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method for mitigating inter cell interferenceand a device therefor.

BACKGROUND ART

A wireless communication system has been widely developed to providevarious kinds of communication services such as voice and data.Generally, the wireless communication system is a multiple access systemthat can support communication with multiple users by sharing availablesystem resources (bandwidth, transmission power, etc.). Examples of themultiple access system include a code division multiple access (CDMA)system, a frequency division multiple access (FDMA) system, a timedivision multiple access (TDMA) system, an orthogonal frequency divisionmultiple access (OFDMA) system, and a single carrier frequency divisionmultiple access (SC-FDMA) system.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the conventionalproblem is to provide a method for efficiently mitigating inter cellinterference in a wireless communication system and a device therefor.Another object of the present invention is to provide a method forscheduling for mitigation of inter cell interference and a devicetherefor.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

In one aspect of the present invention, a method for receiving adownlink signal in a user equipment of a wireless communication systemcomprises the steps of receiving a physical downlink control channel(PDCCH) signal, which includes scheduling information, from a basestation on a first subframe; receiving a physical downlink sharedchannel (PDSCH) signal corresponding to the PDCCH signal from the basestation on a second subframe; and decoding the PDSCH signal, wherein aninterval between the first subframe and the second subframe is varied.

In another aspect of the present invention, a user equipment for use ina wireless communication system comprises a radio frequency (RF) unit;and a processor, wherein the processor is configured to receive aphysical downlink control channel (PDCCH) signal, which includesscheduling information, from a base station on a first subframe, receivea physical downlink shared channel (PDSCH) signal corresponding to thePDCCH signal from the base station on a second subframe, and decode thePDSCH signal, and an interval between the first subframe and the secondsubframe is varied.

Preferably, the interval between the first subframe and the secondsubframe is varied by predetermined information within the PDCCH signal.

Preferably, the interval between the first subframe and the secondsubframe is varied by considering at least one of carrier configurationfor the user equipment and a value of a carrier indication field withinthe PDCCH signal.

Preferably, if a single carrier is configured for the user equipment,the value of the carrier indication field is used to indicate the secondsubframe, if a multi-carrier is configured for the user equipment, thevalue of the carrier indication field is used to indicate a carrier towhich the PDSCH signal is transmitted, and the first subframe and thesecond subframe are given equally.

Preferably, if a single carrier is configured for the user equipment,the value of the carrier indication field is used to indicate the secondsubframe, and if a multi-carrier is configured for the user equipment,the value of the carrier indication field is used to indicatecombination of the carrier to which the PDSCH signal is transmitted andthe second subframe.

Preferably, the processor is further configured to transmit a physicaluplink control channel (PUCCH) signal, which includes receptionacknowledgement information for the PDSCH signal, on a third subframe, aresource for the PUCCH signal is inferred from a resource used totransmit the PDCCH, and an index of the third subframe is inferred fromthat of the second subframe used to transmit the PDSCH signal.

Preferably, the processor is further configured to transmit a PUCCHsignal, which includes reception acknowledgement information for thePDSCH signal, on a third subframe, and transmission of the PUCCH signalis dropped on the third subframe if an interval between the secondsubframe and the third subframe is smaller than a predetermined value.

Advantageous Effects

According to the present invention, inter cell interference mayefficiently be mitigated in the wireless communication system. Also, thepresent invention may provide scheduling for mitigation of inter cellinterference.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a diagram illustrating physical channels used in a 3^(rd)generation partnership project long term evolution (3GPP LTE) system,which is an example of a wireless communication system, and a generalmethod for transmitting a signal using the physical channels;

FIG. 2A is a diagram illustrating a structure of a radio frame;

FIG. 2B is a diagram illustrating a resource grid of a downlink slot;

FIG. 3 is a diagram illustrating a structure of a downlink frame;

FIG. 4 is a diagram illustrating a structure of an uplink subframe;

FIG. 5 is a diagram illustrating an example of determination of PUCCHresources for acknowledgement (ACK)/negative ACK (NACK);

FIG. 6 is a diagram illustrating a carrier aggregation (CA)communication system;

FIG. 7 is a diagram illustrating an example of cross-carrier scheduling;

FIG. 8 is a diagram illustrating a coordinated multi point (CoMP)transmission system;

FIG. 9 is a diagram illustrating an example of a dominant interferenceenvironment;

FIG. 10 is a diagram illustrating an example of inter cell interferencebased on a physical channel in a dominant interference environment;

FIG. 11 is a diagram illustrating a method for mitigating inter cellinterference according to the embodiment of the present invention;

FIG. 12 is a diagram illustrating a method for scheduling a PDSCH bycontrolling a carrier (or subframe) indicator value in case of TDD UL/DLconfiguration 1;

FIG. 13 is a diagram illustrating an example of a reporting operation ofACK/NACK for multi-subframe scheduling through dummy DL allocation in anFDD system;

FIG. 14 is a diagram illustrating a multi-subframe scheduling method ina multi-carrier status; and

FIG. 15 is a diagram illustrating a base station and a user equipment,which can be applied to the embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following technology may be used for various wireless accesstechnologies such as CDMA (code division multiple access), FDMA(frequency division multiple access), TDMA (time division multipleaccess), OFDMA (orthogonal frequency division multiple access), andSC-FDMA (single carrier frequency division multiple access). The CDMAmay be implemented by the radio technology such as UTRA (universalterrestrial radio access) or CDMA2000. The TDMA may be implemented bythe radio technology such as global system for mobile communications(GSM)/general packet radio service (GPRS)/enhanced data rates for GSMevolution (EDGE). The OFDMA may be implemented by the radio technologysuch as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, andevolved UTRA (E-UTRA). The UTRA is a part of a universal mobiletelecommunications system (UMTS). A 3^(rd) generation partnershipproject long term evolution (3GPP LTE) is a part of an evolved UMTS(E-UMTS) that uses E-UTRA, and adopts OFDMA in a downlink and SC-FDMA inan uplink. LTE-advanced (LTE-A) is an evolved version of the 3GPP LTE.

For clarification of the description, the following embodiments will bedescribed based on that technical features of the present invention areapplied to the 3GPP LTE/LTE-A. However, it is to be understood that thetechnical spirits of the present invention are not limited to the 3GPPLTE/LTE-A. Also, specific terminologies used hereinafter are provided toassist understanding of the present invention, and various modificationsmay be made in the specific terminologies within the range that does notdepart from the technical spirits of the present invention.

In a wireless communication system, a user equipment may receiveinformation from a base station through a downlink (DL), and may alsotransmit information to the base station through an uplink (UL).Examples of information transmitted from and received between the userequipment and the base station include data and various kinds of controlinformation. Various physical channels exist depending on types andusage of information transmitted from or received between the userequipment and the base station.

FIG. 1 is a diagram illustrating physical channels used in a 3^(rd)generation partnership project long term evolution (3GPP LTE) system,which is an example of a mobile communication system, and a generalmethod for transmitting a signal using the physical channels.

A user equipment performs initial cell search such as synchronizing witha base station when it newly enters a cell or the power is turned on, atstep S101. To this end, the user equipment may synchronize with the basestation by receiving a primary synchronization channel (P-SCH) and asecondary synchronization channel (S-SCH) from the base station, and mayacquire information of cell ID, etc. Afterwards, the user equipment mayacquire broadcast information within a cell by receiving a physicalbroadcast channel from the base station. Meanwhile, the user equipmentmay identify the channel status of a downlink by receiving a downlinkreference signal (DL RS) in the initial cell search step.

The user equipment which has finished the initial cell search mayacquire more detailed system information by receiving a physicaldownlink control channel (PDCCH) and a physical downlink control channel(PDSCH) based on the physical downlink control channel information, atstep S102.

Afterwards, the user equipment may perform a random access procedure(RACH) for the base station, such as step S103 to S106, to completelyaccess the base station. To this end, the user equipment may transmit apreamble through a random physical random access channel (PRACH) (S103),and may receive a response message to the preamble through the PDCCH anda PDSCH corresponding to the PDCCH (S104). In case of contention basedrandom access, a contention resolution procedure such as transmission(S105) of additional PRACH and reception (S106) of the PDCCH and thePDSCH corresponding to the PDCCH may be performed.

The user equipment which has performed the aforementioned steps mayreceive the PDCCH/PDSCH (S107) and transmit a physical uplink sharedchannel (PUSCH) and a physical uplink control channel (PUCCH) (S108), asa general procedure of transmitting uplink/downlink signals. The controlinformation transmitted from the user equipment to the base station willbe referred to as uplink control information (UCI). The UCI includeshybrid automatic repeat and request acknowledgement/negativeacknowledgement (HARQ ACK/NACK), a scheduling request (SR), channelstate information (CSI), etc. In this specification, the HARQ ACK/NACKwill simply be referred to as HARQ-ACK or ACK/NACK(A/N). HARQ-ACKincludes at least one of positive ACK (simply, ACK), negative ACK(NACK), discontinuous transmission (DTX) and NACK/DTX. CSI includes aCQI (Channel Quality Indicator), a PMI (Precoding Matrix Indicator), RI(Rank Indication), etc. Although the UCI is transmitted through thePUCCH, it may be transmitted through the PUSCH if control informationand traffic data should be transmitted at the same time. Also, the userequipment may non-periodically transmit the UCI through the PUSCH inaccordance with request/command of the network.

FIG. 2A is a diagram illustrating a structure of a radio frame. In acellular OFDM wireless packet communication system, uplink/downlink datapacket transmission is performed in a subframe unit, wherein onesubframe is defined by a given time interval that includes a pluralityof OFDM symbols. The 3GPP LTE standard supports a type 1 radio framestructure applicable to frequency division duplex (FDD) and a type 2radio frame structure applicable to time division duplex (TDD).

FIG. 2A(a) is a diagram illustrating a structure of a type 1 radioframe. The downlink radio frame includes 10 subframes, each of whichincludes two slots in a time domain. A time required to transmit onesubframe will be referred to as a transmission time interval (TTI). Forexample, one subframe may have a length of 1 ms, and one slot may have alength of 0.5 ms. One slot includes a plurality of OFDM symbols in timedomain and a plurality of resource blocks (RB) in frequency domain.Since OFDMA is used on a downlink in the 3GPP LTE system, OFDM symbolsrepresent one symbol interval. The OFDM symbols may be referred to asSC-FDMA symbols or symbol interval. The resource block as resourceallocation unit may include a plurality of continuous subcarriers in oneslot.

The number of OFDM symbols included in one slot may be varied dependingon configuration of cyclic prefix (CP). Examples of the CP includeextended CP and normal CP. For example, if the OFDM symbols areconfigured by normal CP, the number of OFDM symbols included in one slotmay be 7. If the OFDM symbols are configured by extended CP, since thelength of one OFDM symbol is increased, the number of OFDM symbolsincluded in one slot is smaller than that of OFDM symbols in case ofnormal CP. In case of the extended CP, the number of OFDM symbolsincluded in one slot may be 6. If a channel status is unstable like thecase where the user equipment moves at high speed, the extended CP maybe used to reduce inter-symbol interference.

If the normal CP is used, since one slot includes seven OFDM symbols,one subframe includes 14 OFDM symbols. At this time, first two or threeOFDM symbols of each subframe may be allocated to a physical downlinkcontrol channel (PDCCH), and the other OFDM symbols may be allocated toa physical downlink shared channel (PDSCH).

FIG. 2A(b) is a diagram illustrating a structure of a type 2 radioframe. The type 2 radio frame includes two half frames, each of whichincludes four normal subframes and a special subframe. The specialsubframe includes a downlink pilot time slot (DwPTS), a guard period(GP), and an uplink pilot time slot (UpPTS). Each subframe includes twoslots. In the special subframe, DwPTS is used for initial cell search,synchronization or channel estimation at the user equipment. UpPTS isused to synchronize channel estimation at the base station with uplinktransmission of the user equipment. Also, the guard period is to removeinterference occurring in the uplink due to multipath delay of downlinksignals between the uplink and the downlink.

The aforementioned structure of the radio frame is only exemplary, andvarious modifications may be made in the number of subframes included inthe radio frame, the number of slots included in the subframe, or thenumber of symbols included in the slot.

FIG. 2B is a diagram illustrating a resource grid of a downlink slot.

Referring to FIG. 2B, the downlink slot includes a plurality of OFDMsymbols in a time region. One downlink slot includes 7(6) OFDM symbols,and a resource block includes 12 subcarriers in a frequency domain. Eachelement on the resource grid will be referred to as a resource element(RE). One resource block (RB) includes 12×7(6) resource elements. Thenumber N_(RB) of resource blocks (RBs) included in the downlink slotdepends on a downlink transmission bandwidth. A structure of an uplinkslot is the same as that of the downlink slot except that OFDM symbolsare replaced with SC-FDMA symbols.

FIG. 3 is a diagram illustrating a structure of a downlink subframe.

Referring to FIG. 3, maximum 3(4) OFDM symbols located at the front ofthe first slot of the subframe correspond to a control region to which acontrol channel is allocated. The other OFDM symbols correspond to adata region to which a physical downlink shared channel (PDSCH) isallocated. Examples of the downlink control channel used in the LTEinclude a PCFICH (Physical Control Format Indicator CHannel), a PDCCH(Physical Downlink Control CHannel), and a PHICH (Physical Hybrid ARQIndicator CHannel). The PCFICH is transmitted from the first OFDM symbolof the subframe, and carries information on the number of OFDM symbolsused for transmission of the control channel within the subframe. ThePHICH carries HARQ ACK/NACK (acknowledgement/negative-acknowledgement)in response to uplink transmission.

The control information transmitted through the PDCCH will be referredto as downlink control information (DCI). The DCI includes resourceallocation information for a user equipment or user equipment group andother control information. For example, the DCI includes uplink/downlinkscheduling information, uplink transmission (Tx) power control command,etc.

The PDCCH carries transport format and resource allocation informationof a downlink shared channel (DL-SCH), transport format and resourceallocation information of an uplink shared channel (UL-SCH), paginginformation on a paging channel (PCH), system information on the DL-SCH,resource allocation information of higher layer control message such asrandom access response transmitted on the PDSCH, a set of transmissionpower control commands of individual user equipments (UEs) within a userequipment group, a transmission power control command, and activityindication information of voice over Internet protocol (VoIP). Aplurality of PDCCHs may be transmitted within the control region. Theuser equipment may monitor the plurality of PDCCHs. The PDCCH istransmitted on aggregation of one or a plurality of continuous controlchannel elements (CCEs). The CCE is a logic allocation unit used toprovide a coding rate based on the status of a radio channel to thePDCCH. The CCE corresponds to a plurality of resource element groups(REGs). The format of the PDCCH and the number of bits of the PDCCH aredetermined depending on the number of CCEs. The base station determinesa PDCCH format depending on the DCI to be transmitted to the userequipment, and attaches cyclic redundancy check (CRC) to the controlinformation. The CRC is masked (or scrambled) with an identifier (forexample, radio network temporary identifier (RNTI)) depending on usageof the PDCCH or owner of the PDCCH. For example, if the PDCCH is for aspecific user equipment, an identifier (for example, cell-RNTI (C-RNTI))of the corresponding user equipment may be masked with the CRC. If thePDCCH is for a paging message, a paging identifier (for example,Paging-RNTI (P-RNTI)) may be masked with the CRC. If the PDCCH is forsystem information (in more detail, system information block (SIB)),system information RNTI (SI-RNTI) may be masked with the CRC. If thePDCCH is for a random access response, a random access RNTI (RA-RNTI)may be masked with the CRC.

FIG. 4 is a diagram illustrating a structure of an uplink subframe in anLTE system.

Referring to FIG. 4, the uplink subframe includes a plurality of slots(for example, two). Each slot may include a plurality of SC-FDMAsymbols, wherein the number of SC-FDMA symbols included in each slot isvaried depending on a cyclic prefix (CP) length. The uplink subframe isdivided into a data region and a control region in a frequency domain.The data region includes a PUSCH, and is used to transmit a data signalsuch as voice. The control region includes a PUCCH, and is used totransmit uplink control information (UCI). The PUCCH includes RB pairlocated at both ends of the data region on a frequency axis, andperforms hopping on the border of the slots.

The PUCCH may be used to transmit the following control information.

-   -   SR (Scheduling Request): is information used to request uplink        UL-SCH resource. The SR is transmitted using an on-off keying        (OOK) system.    -   HARQ ACK/NACK: is a response signal to a downlink data packet on        the PDSCH. It represents whether the downlink data packet has        been successfully received. ACK/NACK 1 bit is transmitted in        response to a single downlink codeword, and ACK/NACK 2 bits are        transmitted in response to two downlink codewords.    -   CSI (Channel State Information): is feedback information on a        downlink channel. The CSI includes channel quality indicator        (CQI), and MIMO (Multiple Input Multiple Output) related        feedback information includes a rank indicator (RI) and a        precoding matrix indicator (PMI). 20 bits are used per subframe.

The quantity of the uplink control information (UCI) that may betransmitted from the user equipment for the subframe depends on thenumber of SC-FDMA symbols available for control informationtransmission. The SC-FDMA symbols available for control informationtransmission mean the remaining SC-FDMA symbols except for SC-FDMAsymbols for reference signal transmission for the subframe, and the lastSC-FDMA symbol of the subframe is excluded in case of the subframe forwhich a sounding reference signal (SRS) is set. The reference signal isused for coherent detection of the PUCCH. The PUCCH supports sevenformats in accordance with information which is transmitted.

Table 1 illustrates a mapping relation between the PUCCH format and theUCI in the LTE system.

TABLE 1 PUCCH Format Uplink Control Information (UCI) Format 1Scheduling request (SR) (unmodulated waveform) Format 1a 1-bit HARQACK/NACK with/without SR Format 1b 2-bit HARQ ACK/NACK with/without SRFormat 2 CQI (20 coded bits) Format 2 CQI and 1- or 2-bit HARQ ACK/NACK(20 bits) for extended CP only Format 2a CQI and 1-bit HARQ ACK/NACK(20 + 1 coded bits) Format 2b CQI and 2-bit HARQ ACK/NACK (20 + 2 codedbits)

FIG. 5 is a diagram illustrating an example of determining PUCCHresources for ACK/NACK. In the LTE system, PUCCH resources for ACK/NACKare not previously allocated to each user equipment but used per timingpoint by a plurality of user equipments within a cell. In more detail,the PUCCH resources used for ACK/NACK transmission by the user equipmentcorrespond to PDCCH carrying scheduling information of correspondingdownlink data. In each downlink subframe, an entire region where thePDCCH is transmitted includes a plurality of control channel elements(CCEs), and the PDCCH transmitted to the user equipment includes one ormore CCEs. The user equipment transmits ACK/NACK through a PUCCHresource corresponding to a specific CCE (for example, first CCE) amongCCEs constituting PDCCH received therein.

Referring to FIG. 5, it is assumed that PDSCH information is transferredthrough a PDCCH that includes CCEs Nos. 4 to 6. In this case, the userequipment transmits ACK/NACK through PUCCH No. 4 corresponding to CCENo. 4 which is the first CCE of the PDCCH. FIG. 5 illustrates thatmaximum M number of PUCCHs exist in the uplink (UL) when maximum Nnumber of CCEs exist in the downlink (DL).

In more detail, in the LTE system, the PUCCH resource index is definedas follows.

n ⁽¹⁾ _(PUCCH) =n _(CCE) +N ⁽¹⁾ _(PUCCH)  [Equation 1]

In this case, n⁽¹⁾ _(PUCCH) represents a PUCCH resource index fortransmitting ACK/NACK, N⁽¹⁾ _(PUCCH) represents a signaling valuetransferred from an higher layer, and n_(CCE) represents the smallestvalue of CCE indexes used for PDCCH transmission. A cyclic shift forPUCCH formats 1a/1b, an orthogonal spreading code and a physicalresource block (PRB) are obtained from n⁽¹⁾ _(PUCCH).

FIG. 6 is a diagram illustrating a carrier aggregation (CA)communication system. The LTE-A system uses the carrier aggregationtechnology or the bandwidth aggregation technology, which uses wideruplink/downlink bandwidth through a plurality of uplink/downlinkfrequency blocks, to use wider frequency bandwidth. Each frequency blockis transmitted using a component carrier (CC). The component carrier maybe understood as carrier frequency (or center carrier or centerfrequency) for a corresponding frequency block.

Referring to FIG. 6, a plurality of uplink/downlink component carriers(CC) may be collected to support wider uplink/downlink bandwidth. Therespective CCs may adjoin each other or not in the frequency domain. Abandwidth of each component carrier may be defined independently.Asymmetric carrier aggregation where the number of UL CCs is differentfrom the number of DL CCs may be performed. For example, if the numberof DL CCs is 2 and the number of UL CCs is 1, carrier aggregation may beconfigured to correspond to 2:1. DL CC/UL CC links may be fixed to thesystem or may be configured semi-statically. Also, even though a systemfull band includes N number of CCs, a frequency band that may bemonitored and received by a specific user equipment may be limited toM(<N) number of CCs. Various parameters for carrier aggregation may beconfigured cell-specifically, user equipment group-specifically, or userequipment-specifically. Meanwhile, the control information may be set tobe transmitted and received through a specific CC only. This specific CCmay be referred to as a primary CC (PCC) (or anchor CC), and the otherCCs may be referred to as secondary CCs (SCC).

The LTE-A system uses a concept of cell to manage radio resources. Thecell is defined by combination of downlink resources and uplinkresources, wherein the uplink resources may be defined selectively.Accordingly, the cell may be configured by downlink resources only, ormay be configured by downlink resources and uplink resources. If carrieraggregation is supported, linkage between carrier frequency (or DL CC)of the downlink resources and carrier frequency (or UL CC) of the uplinkresources may be indicated by system information. The cell operated onthe primary frequency (or PCC) may be referred to as a primary cell(PCell), and the cell operated on the secondary frequency (or SCC) maybe referred to as a primary cell (PCell). The PCell is used such thatthe user equipment performs an initial connection establishmentprocedure or connection re-establishment procedure. The PCell may referto a cell indicated during a handover procedure. The SCell may beconfigured after RRC connection is established, and may be used toprovide an additional radio resource. The PCell and the SCell may bereferred to as serving cells. Although the user equipment is inRRC-CONNECTED state, if it is not set by carrier aggregation or does notsupport carrier aggregation, a single serving cell configured by the Pcell only exists. On the other hand, if the user equipment is in theRRC-CONNECTED state and is set by carrier aggregation, one or moreserving cells may exist, wherein the serving cells may include the PCelland full SCells. After an initial security activity procedure starts,for the user equipment supporting carrier aggregation, the network mayconfigure one or more SCells in addition to the PCell initiallyconfigured during a connection establishment procedure.

If cross-carrier scheduling (or cross-CC scheduling) is used, the PDCCHfor downlink allocation is transmitted to DL CC#0, and the correspondingPDSCH may be transmitted to DL CC#2. For cross-carrier scheduling,introduction of a carrier indicator field (CIF) may be considered. Thepresence of CIF within the PDCCH may be configured by higher layersignaling (for example, RRC signaling) semi-statically and userequipment-specifically (or user equipment group-specifically). The baseline of PDCCH transmission will be summed up as follows.

-   -   CIF disabled: the PDCCH on the DL CC allocates PDSCH resource on        the same DL CC or PUSCH resource on one linked UL CC.    -   CIF enabled: the PDCCH on the DL CC may allocate PDSCH or PUSCH        resource on a specific DL/UL CC among a plurality of aggregated        DL/UL CCs by using the CIF.

If the CIF exists, the base station may allocate a PDCCH monitoring DLcell set to reduce load of blind decoding (BD) in view of the userequipment. The PDCCH monitoring DL cell set includes one or more DL CCsas a part of the aggregated DL CCs, and the user equipment detects anddecodes the PDCCH on the corresponding DL CC only. In other words, ifthe base station schedules the PDSCH/PUSCH to the user equipment, thePDCCH is transmitted through the PDCCH monitoring DL CC set only. ThePDCCH monitoring DL CC set may be configured userequipment-specifically, user equipment group-specifically orcell-specifically. The terms “PDCCH monitoring DL CC” may be replacedwith the equivalent terms such as monitoring carrier and monitoringcell. Also, CC aggregated for the user equipment may be replaced withthe equivalent terms such as serving CC, serving carrier, and servingcell.

FIG. 7 is a diagram illustrating scheduling when a plurality of carriersare aggregated. It is assumed that three DL cells are aggregated. It isalso assumed that DL CC A is set to a PDCCH monitoring DL CC. DL CC A toDL CC C may be referred to as serving CCs, serving carriers, servingcells, etc. If the CIF is disabled, each DL CC may transmit the PDCCHonly that schedules PDSCH of the DL CC without CIF in accordance withthe LTE PDCCH rule. On the other hand, if the CIF is enabled by userequipment-specific (or user equipment group-specific or cell-specific)higher layer signaling, the DL CC A (monitoring DL CC) may transmit thePDCCH, which schedules the PDSCH of another CC, as well as the PDCCH,which schedules the PDSCH of the DL CC A. In this case, the PDCCH is nottransmitted from the DL CC B/C which is not set to the PDCCH monitoringDL CC.

In the meantime, it is expected that the LTE-A system, which is thestandard of the next generation wireless communication system, willsupport a coordinated multi point (CoMP) transmission system, which hasnot been supported by the existing standard, so as to improve a datatransmission rate. In this case, the CoMP transmission system means thattwo or more base stations or cells perform communication with a userequipment by coordinating with each other to improve communicationthroughput between the base station (cell or sector) and the userequipment located in a shaded zone.

Examples of the CoMP system may include a coordinated MIMO type jointprocessing (CoMP-JP) system through data sharing and a CoMP-coordinatedscheduling/beamforming (CoMP-CS/CB) system.

In case of the down link, according to the joint processing (CoMP-JP)system, the user equipment may simultaneously receive data from eachbase station that performs CoMP transmission system, and may improvereceiving throughput by combining the signals received from each basestation (joint transmission; JT). Also, there may be considered a method(dynamic point selection, DPS) for transmitting data from one of basestations, which perform the CoMP transmission system, to the userequipment at a specific time. According to the coordinatedscheduling/beamforming (CoMP-CS/CB) system, the user equipment maymomentarily receive data from one base station, that is, serving basestation, through beamforming.

FIG. 8 is a diagram illustrating a coordinated multi point (CoMP)transmission system. In FIG. 8, it is assumed that the user equipment,that is, CoMP user equipment is operated by receiving controlinformation from the serving base station (serving eNB, s-eNB). Also, inFIG. 8, it is assumed that data information is simultaneouslytransmitted from the s-eNB and a cooperative base station (eNB or c-eNB)in accordance with the CoMP JP scheme. If the CoMP CS/CB scheme is used,the data information is transmitted from the s-eNB only. In case of theDPS, the data information is transmitted from the base station onlyselected dynamically within the cooperative set that includes s-eNB andone or more c-eNBs. In the CoMP transmission system, the base stationmay be replaced with the terms such as cell and point.

Although FIG. 8 illustrates only one c-eNB, the present invention maygenerally be applied to the cooperative cell set where a plurality ofc-eNBs exist. Also, the present invention may be applied to aninter-site CoMP structure that s-eNB and c-eNB are locally spaced apartfrom each other as shown in FIG. 8, an intra-site CoMP structure thateNBs existing within the cooperative cell set are co-located, or aheterogeneous network structure that is a combination type of theinter-site CoMP structure and the intra-site CoMP structure.

For the aforementioned CoMP transmission, higher CSI exactness will berequired. For example, in case of the CoMP JT system, since several basestations transmit same data to a specific user equipment in cooperationwith one another, the CoMP JT system may be regarded as a MIMO systemthat antennas are distributed geographically. Accordingly, in case ofMU-MIMO based on the JT, CSI exactness of high level will be required inthe same manner as single cell MU-MIMO. Also, in case of the CoMP CBsystem, elaborate CSI will be required to avoid interference of aneighboring cell to a serving cell.

An CoMP operation which mitigates inter cell interference is moreeffective in a dominant environment where an interference cell, whichcauses stronger interference than that of the serving cell, exists. Thisis because that dominant interference may effectively be mitigatedthrough a proper CoMP operation.

FIG. 9 is a diagram illustrating an example of a dominant interferenceenvironment.

In FIG. 9( a), although the user equipment receives a stronger signalfrom a cell 2, the cell 2 connects the corresponding user equipment to acell 1 where a weaker signal is received, to obtain off loading effect.This operation may be performed in such a manner that handover bias tothe cell 1 is set at a proper level to allow a final handover referencevalue with bias to be greater than the cell 2 although a signal of thecell 1 is lower than that of the cell 2. In this case, if the cell 1 isa pico cell, it is especially useful in that load of the cell 2, whichis a macro cell that should provide services to many user equipments,may be reduced. In FIG. 9( b), although the user equipment receives astronger signal from the cell 2, the cell 2 is a closed subscriber group(CSG) cell that cannot be accessed by the user equipment. In this case,even though the signal of the cell 2 is strong, since the correspondinguser equipment is not permitted to access the cell 2, it should beconnected with the cell 1, which is one of the other cells, to performcommunication.

FIG. 10 is a diagram illustrating an example of inter cell interferencebased on a physical channel in a dominant interference environment.

Referring to FIG. 10, in case of a downlink data channel, CoMPcoordinated beamforming (CB) operation may be effective to solve intercell interference. Through CB operation, an interference cell mayperform beamforming in a specific direction that may minimizeinterference on a victim user equipment (UE), whereby the victim userequipment may be affected at a very low level by interference from adata channel of the interference cell. However, in case of the downlinkcontrol channel, it is general that transmission diversity is used toenable stable transmission and reception even without channelinformation. For this reason, it is difficult to apply the CB operationto the downlink control channel. If transmission diversity is used, thecell transmits its control channel through beams formed uniformly in alldirections on a spatial domain, whereby the cell cannot transmit asignal in only the specific direction that may minimize interference onthe victim user equipment. Accordingly, although the data channel (forexample, PDSCH) of the interference cell for a specific subframe maymaintain interference on the victim user equipment at a low levelthrough CB, a control channel (for example, PDCCH) of the interferencecell, which transfers information for scheduling the PDSCH of theinterference cell, may cause high interference to the victim userequipment. As a result, for the corresponding subframe, the victim userequipment may receive the PDSCH of the serving cell as interference fromthe PDSCH of the interference cell is low, but fails to receive thePDCCH of the serving cell due to strong interference from the PDCCH ofthe interference cell. For this reason, a problem may occur in that thevictim user equipment may not receive even the PDSCH of the servingcell.

Hereinafter, solutions for the aforementioned problem will be describedwith reference to the accompanying drawing.

FIG. 11 is a diagram illustrating a method for mitigating inter cellinterference according to the embodiment of the present invention.

Referring to FIG. 11, the interference cell may transmit a PDCCHcorresponding to a PDSCH transmitted for a specific subframe, for one ofprevious subframes not the subframe for which the corresponding PDSCH istransmitted. In other words, the interference cell may schedule thePDSCH of the subframe n through a PDCCH of a subframe (n−m) (m>0), andmay not transmit any signal through a resource for PDCCH for thesubframe n or may not transmit some signal (for example, PDCCH signalcorresponding to the PDSCH). For this reason, the victim user equipmentmay receive the PDCCH of the serving cell without interference.According to this method, since PDSCHs of several subframes may bescheduled by the PDCCH of one subframe, the operation suggested in thismethod will be referred to as “multi-subframe scheduling” or“inter-subframe scheduling”.

Hereinafter, a communication scheme required for a correct operation ofmulti-sbuframe scheduling will be suggested in more detail.

Method for Indicating Subframe

For multi-subframe scheduling, a field indicating PDSCH/PUSCH of acorresponding subframe to which a corresponding PDCCH corresponds willbe required. For convenience, information indicating a subframecorresponding to the PDCCH in multi-subframe scheduling will be referredto as a subframe indicator or a resource indicator. The subframeindicator may newly be defined within the DCI or may bedefined/indicated using a part of the existing DCI. Similarly, thesubframe indicator may be transmitted through a field (for convenience,subframe indication field or resource indication field) newly definedwithin the DCI, or may be transmitted using a part of the existing DCIfield. For example, the subframe indicator may be transmitted using afield (for example, CIF field) defined for cross-carrier scheduling. Inthis case, a DCI format of the PDCCH, which is used for multi-subframescheduling, may be designed to have the same structure as that of theDCI format of the PDCCH for cross-carrier scheduling. In other words, acarrier indicator for cross-carrier scheduling may be used as thesubframe indicator depending on the status. In order to assistunderstanding of the present invention, the carrier indicator may beused to refer to the subframe indicator, and the carrier indicator andthe subframe indicator may be interpreted to indicate carrier orsubframe.

If the same DCI format is used for multi-subframe scheduling andcross-carrier scheduling, a problem as to how to interpret the CIF fieldmay occur. To this end, the present invention suggests that a specificuser equipment interprets a value of a CIF field as a subframe indicatorindicating PDSCH/PUSCH of a subframe scheduled by the correspondingPDCCH if the specific user equipment receives the CIF field in a statethat the specific user equipment is configured to use one CC. Forexample, if the subframe indicator included in the PDCCH of the subframen indicates m, it may be interpreted that the corresponding PDCCHschedules a PDSCH of a subframe (n+m) or a PUSCH of a subframe (n+k+m).In this case, k is a value indicating transmission timing between aPUSCH and a PDCCH (UL grant), which are defined in the 3GPP LTE system.In the FDD system, k=4, and in the TDD system, k depends on UL/DLsubframe configuration.

Table 2 illustrates uplink-downlink configuration in a TDD system of the3GPP LTE, and Table 3 illustrates a difference k in transmission timingbetween the PDCCH and the PUSCH according to TDD UL/DL configuration.

TABLE 2 Downlink- to-Uplink Uplink- Switch- downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U DS U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  DS U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D DD D 6 5 ms D S U U U D S U U D In this case, D represents a DL subframe,U represents a UL subframe, and S represents a special subframe.

TABLE 3 TDD UL/DL DL subframe number n Configuration 0 1 2 3 4 5 6 7 8 90 4 6 4 6 1 6 4 6 4 2 4 4 3 4 4 4 4 4 4 5 4 6 7 7 7 7 5

For the aforementioned operation, the base station may configure thenumber of bits of the carrier (or subframe) indicator of the PDCCHtransmitted to the corresponding user equipment through an higher layersignal such as radio resource control (RRC) signal. Alternatively, thebase station may notify the user equipment of the range (or maximumvalue) of the value of m through the higher layer signal such as RRC. Inother words, the base station may semi-statically configure the range(or maximum value) of multi-subframe scheduling applied to thecorresponding user equipment or the range (or maximum value) of asubframe that may be scheduled for a specific subframe. Through thisconfiguration, the user equipment may simply perform blind decoding forthe PDCCH by means of one assumption of the number of bits of thecarrier (or subframe) indicator.

Although scheduling of the PDSCH existing for one subframe through onePDCCH has been described as above, the scope of the present invention isnot limited to this case. As a modified example of the presentinvention, if the carrier (or subframe) indicator indicates a specificstatus, PDSCH existing for one or more subframes may be scheduledthrough the corresponding PDCCH. For example, it is assumed that 2 bitsare allocated to the carrier (or subframe) indicator and the PDCCH istransmitted for the subframe n. In this case, if the indicator is 00, itmay be interpreted that the PDSCH of the subframe n is scheduled. If theindicator is 01, it may be interpreted that the PDSCH of the subframen+1 is scheduled. If the indicator is 11, it may be interpreted that thePDSCHs of the subframe n and the subframe n+1 are scheduled. Thesubframe indicator included in the PDCCH of the subframe n may include abitmap indicating a subframe having actual downlink resource allocationamong subframes (for example, subframe n, n+1, . . . ) for which thePDSCH may be scheduled. If one PDCCH schedules PDSCHs of two or moresubframes, resource allocation on each PDSCH, modulation and codingscheme (MCS) level, transmission rank and/or precoding information mayindependently be transmitted to the corresponding PDCCH. Alternatively,all or some of the scheduling information may equally be applied to thePDSCHs of all the subframes.

Since DL subframe and UL subframe occur alternately in the TDD system,if the value of the carrier (or subframe) indicator is set to m, it maybe interpreted that the PDCCH of the subframe n schedules the PDSCH ofthe mth DL subframe after the subframe n or the PUSCH of the mth ULsubframe after the subframe (n+k).

FIG. 12 is a diagram illustrating a method for scheduling a PDSCH bycontrolling a carrier (or subframe) indicator value in case of TDD UL/DLconfiguration 1. In the drawing, D represents a DL subframe, Urepresents a UL subframe, and S represents a special subframe.

Referring to FIG. 12, PDSCH scheduling set to m=1 at subframe 0 meansPDSCH scheduling of subframe 1 which is the subframe for which nextPDSCH may be transmitted. PDSCH scheduling set to m=1 at subframe 1means scheduling of subframe 4 which is the first DL subframe for whichnext PDSCH may be transmitted. In the meantime, PUSCH scheduling set tom=1 at subframe 6 means PUSCH scheduling of subframe 3 which is thefirst UL subframe after subframe 2 which is the PUSCH transmissionsubframe according to Table 3. Similarly, PUSCH scheduling set to m=1 atsubframe 9 means PUSCH scheduling of subframe 7 which is the first ULsubframe after subframe 3 which is the PUSCH transmission subframeaccording to Table 3.

Method for Determining PDSCH Start Timing Point

In the existing 3GPP LTE system, the user equipment first reads PCFICHand identifies whether the read PDCCH reserves how many OFDM symbols ofthe corresponding subframe and then receives PDSCH on the assumptionthat the PDSCH is transmitted from next OFDM symbol corresponding to thetime when transmission of PDCCH ends. However, if multi-subframescheduling is used, since subframes which the PDCCH and the PDSCH aretransmitted are varied, a PDSCH start timing point (that is, start OFDMsymbol) of the subframe n+m (m>0) scheduled through the PDCCH of thesubframe n cannot be identified by the existing system. Accordingly, aseparate operation indicating a start timing point of the PDSCH will berequired if multi-subframe scheduling is used.

According to one method, if multi-subframe scheduling is performed, amethod for configuring a start timing point of a PDSCH as an higherlayer signal such as RRC may be used. This method is advantageous inthat the start timing point of the PDSCH may be notified stably and themethod used in cross-carrier scheduling between CCs may be reused. Tothis end, cell 1 and cell 2 in FIG. 10, for example, may exchangeinformation on a start timing point of a PDSCH, which will be used bythe cell 2 for subframes for multi-subframe scheduling, with each otherthrough backhaul signaling between them.

According to another method, a start timing point of the PDSCH at thesubframe n+m may be determined by PCFICH of the subframe n for which thecorresponding PDSCH is scheduled. In other words, the user equipment mayread the PCFICH for the subframe n and identify the location of the OFDMsymbol corresponding to the time when transmission of the PDCCH ends,and may assume that the PDSCH for the subframe n+m is transmitted fromnext symbol of the OFDM symbol identified by the PCFICH of the subframen. This method is advantageous in that the PCFICH of the subframe n iscontrolled to indirectly control a PDSCH start timing point of thesubframe n+m dynamically.

According to other method, the PCFICH may be transmitted even for thesubframe n+m, and the user equipment may calculate the PDSCH starttiming point for the subframe n+m on the basis of the transmission ofthe PCFICH. Referring to FIG. 10, this method is not advantageous inthat some interference is caused due to transmission of the PCFICH fromthe interference cell 2 even for the subframe n+m. However, since thePCFICH reserves a small quantity of resources relatively as comparedwith the PDCCH, this method is advantageous in that interference ismaintained at low level and the PDSCH start timing point of thecorresponding subframe may be controlled directly and dynamically.

Method for Transmitting UL ACK/NACK

In case of the existing 3GPP LTE system, UL ACK/NACK for the decodingresult of the PDSCH transmitted for DL subframe n is transmitted for ULsubframe n+k. In the FDD system, k=4, and in the TDD system, k is asillustrated in Table 4. Also, the location of the PUCCH resource towhich ACK/NACK will be transmitted is determined from CCE index of thePDCCH that has scheduled the corresponding PDSCH as described withreference to FIG. 5 and Equation 1. However, since the PDCCH and thePDSCH are not transmitted for the same subframe in multi-subframescheduling, a problem may occur if the location of the PUCCH resourceand subframe for which UL ACK/NACK will be transmitted is determined inthe same manner as the existing method. For example, if the location ofthe PUCCH resource and subframe for which UL ACK/NACK will betransmitted is determined on the basis of PDCCH (DL grant) transmission,a problem may occur in that the user equipment does not have enough timeto decode the PDSCH or the PUCCH resource may collide with PUCCHresource of another PDSCH. Hereinafter, methods for solving the problemwill be suggested.

Table 4 illustrates a difference k in transmission timing betweenPDCCH/PDSCH and UL ACK/NACK in the TDD system of the 3GPP LTE.

TABLE 4 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 4 6 4 6 1 76 4 7 6 4 2 7 6 4 8 7 6 4 8 3 4 11 7 6 6 5 5 4 12 11 8 7 7 6 5 4 5 12 119 8 7 6 5 4 13 6 7 7 7 7 5

1) Method for Determining UL ACK/NACK Resource

A) Semi-Static Configuration Method

In this method, a method for determining ACK/NACK for multi-subframescheduling semi-statically through an higher layer (for example, RRC)signal will be suggested. In other words, if the user equipment receivesscheduling for the PDSCH received for the subframe n through a PDCCH ofsubframe n−m (m>0), it transmits UL ACK/NACK by using a PUCCH resourcegiven through a separate higher layer signal not the PUCCH resourcelinked to CCE index of the PDCCH. This method is advantageous in thatthere is no collision of PUCCH resources even though CCE(s) of the PDCCHused for multi-subframe scheduling for the subframe n−m is reused totransmit the PDCCH for the subframe n.

B) Method for Using PUCCH Resource Linked to PDCCH CCE Index

In this method, a method for using PUCCH resource linked CCE index of aPDCCH during multi-subframe scheduling in the same manner as theexisting method will be suggested. In this method, since a separateACK/NACK resource is not reserved unlike the above method 1-A, it isadvantageous in that the ACK/NACK resource may be used more effectively.Instead, in this method, an operation for avoiding collision of PUCCHresources will be required. For example, if the PDSCH of the subframe nis scheduled using the PDCCH of the subframe n−m, it may be limited suchthat CCE(s) index of the corresponding PDCCH may not be used for thesubframe n. Moreover, the subframe n may be set as the subframe forwhich the PDCCH is not transmitted.

2) Method for Determining UL ACK/NACK Transmission Subframe

A) Method for Maintaining Transmission Timing of the Existing PDCCH andUL ACK/NACK

In this method, UL ACK/NACK is transmitted for the subframe n+k asdefined in the existing 3GPP LTE even though the PDCCH transmitted forthe subframe n schedules the PDSCH of the subframe n+m (m>0) (forexample, in the FDD system, k=4, and in the TDD system, k is asillustrated in Table 4).

In this case, since the time between PDSCH reception and UL ACK/NACKtransmission becomes short in view of the user equipment, a problem mayoccur in that the sufficient time to decode the PDSCH may not beobtained. For example, in the FDD system of the 3GPP LTE, the userequipment receives the PDCCH and the PDSCH for the same subframe,decodes the PDSCH for 3 ms after receiving the PDSCH, and transmits thedecoded result for the subframe corresponding to 4 ms after receivingthe PDSCH. However, in the multi-subframe scheduling status, the userequipment receives the PDCCH, and receives the PDSCH after m subframe,the time for decoding the PDSCH is reduced to (k−m−1)ms.

In order to solve the aforementioned problem, asynchronous HARQoperation of the downlink may be used. For example, if the userequipment fails to sufficiently decode the PDSCH received throughmulti-subframe scheduling, it transmits NACK signal for the subframedefined in the 3GPP LTE. Alternatively, in order to reduce batteryconsumption of the user equipment, if decoding time does not reach 3 ms,it may be ruled such that the user equipment cannot transmit ULACK/NACK. The base station may perform retransmission of the PDSCH byusing the same HARQ process ID after time passes (in this case,retransmission may be performed by multi-subframe scheduling or theexisting scheduling). The user equipment may notify the base station ofthe received result by reporting the decoding result of initialtransmission and retransmission at the time when it transmits ACK/NACKfor retransmission. In particular, if the base station does not allocateany resource to the actual PDSCH from the PDCCH that schedulesretransmission (this may be referred to as dummy DL allocation or dummyPDCCH), it may be interpreted as a message requesting UL ACK/NACK onlyfor initial transmission based on multi-subframe scheduling withoutadditional PDSCH retransmission.

FIG. 13 is a diagram illustrating an example of a reporting operation ofACK/NACK for multi-subframe scheduling through dummy DL allocation in anFDD system.

Referring to FIG. 13, the base station performs multi-subframescheduling for the PDSCH by setting m=1 for DL subframe 0. Although thecorresponding PDSCH is transmitted for DL subframe 1, since the userequipment should transmit ACK/NACK for UL subframe 4, the decoding timebecomes 2 ms. Accordingly, since the user equipment fails to decode thePDSCH for subframe 4, it transmits NACK, or determines that the decodingtime is not sufficient and does not transmit any ACK/NACK. The basestation again transmits dummy PDCCH for subframe 8, and the userequipment that has received the dummy PDCCH reports the decoding resultof the PDSCH for subframe 2 of next radio frame by using PUCCH resourcecorresponding to CCE index of the dummy PDCCH.

B) Method for Determining UL ACK/NACK Transmission Timing to AssureDecoding Time of PDSCH

In this method, if the PDCCH transmitted for the subframe n schedulesthe PDSCH of subframe n+m (m>0), UL ACK/NACK may be transmitted forsubframe n+k'. In this case, k′ is set to assure the time for decodingthe PDSCH. Supposing that 3 ms is required for PDSCH decoding, thesubframe n+k′ may be set to be the first UL subframe after subframen+m+3. As another method, k′=m+k may be determined, wherein k may mean aparameter indicating timing difference between the subframe (that is,subframe n+m) for which the PDSCH is transmitted and the subframe forwhich UL ACK/NACK for the PDSCH is transmitted. This method may beinterpreted that UL ACK/NACK transmission timing is selected by thePDSCH transmission timing not the PDCCH transmission timing ifmulti-subframe scheduling is performed. In the FDD system, k′=m+4 may befixed. It is assumed that the UL ACK/NACK transmission timing isdetermined to assure the decoding time of the PDSCH in accordance withthe aforementioned methods. In this case, if ACK/NACK is transmittedusing the PUCCH resource linked to CCE index of the PDCCH as describedin 2)-B, it is characterized in that ACK/NACK transmission timing isdetermined by the transmission timing (subframe n+m) of the PDSCH butthe PUCCH resource is determined by the transmission timing (subframe n)of the PDCCH.

In some TDD UL/DL subframe configuration, the second DL subframe mayexist between the PDCCH and the UL ACK/NACK subframe, and the sufficientdecoding time may exist between the second DL subframe and the ULACK/NACK subframe. For example, in case of UL/DL configuration 1 of m=0,ACK/NACK for the PDSCH transmitted for DL subframe 0 is transmitted forUL subframe 7 after seven subframes, and at the same time ACK/NACK forthe PDSCH transmitted for subframe 1 is transmitted for UL subframe 7after six subframes. Accordingly, even though the base station sets thesubframe indicator to m=1 for subframe 0 and schedules PDSCHtransmission of subframe 1, the sufficient decoding time exists forsubframe 7 for UL ACK/NACK transmission of subframe 0, and there is noproblem in ACK/NACK transmission for subframe 7 by using the PUCCHresource linked to the PDCCH transmitted for subframe 0. In this case,the subframe for which UL ACK/NACK is transmitted becomes the same as ULACK/NACK subframe of the 3GPP LTE, which is linked to the PDCCH (thatis, k′=k). For convenience, in case of the TDD system, multi-subframescheduling may be limited to subframe of Table 5 of k′=k (that is, thePDSCH of the subframe n+m is scheduled for the subframe n and ULACK/NACK is transmitted for the subframe n+k by using k illustrated inTable 4).

Table 5 illustrates a set of values of m that may assure decoding timeof the PDSCH based on multi-subframe scheduling during ACK/NACKfeedback.

TABLE 5 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 0 0 0 0 10, 1 0 0 0, 1 0 0 2 0, 1, 2 0, 1 0 0, 1, 2, 3 0, 1, 2 0, 1 0 0, 1, 2, 33 0 0, 1, 2, 3, 4 0, 1, 2, 3 0, 1, 2 0, 1, 2 0, 1 0, 1 4 0, 1, 2, 3, 0,1, 2, 3, 0, 1, 2, 3, 4 0, 1, 2, 3 0, 1, 2, 3 0, 1, 2 0, 1 0 4, 5, 6 4, 55 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 4 0, 1, 2, 3 0, 1, 20, 1 0 0, 1, 2, 3, 4, 5, 6, 7 4, 5, 6 4, 5 4, 5, 6, 7, 8 6 0, 1 0 0, 1 00

Additionally, DL subframes applied to multi-subframe scheduling in theTDD system may be limited to DL subframes that transmit UL ACK/NACK forthe same UL subframe in accordance with UL ACK/NACK transmission rule(that is, Table 4) of the 3GPP LTE.

Also, multi-subframe scheduling may be limited to the subframes of k′=kas illustrated in Table 6 below in the same manner as the aforementioneddescription. Table 6 illustrates a set of values of m that may assuredecoding time of the PDSCH based on multi-subframe scheduling for DLsubframe index (case where DL subframes to which multi-subframescheduling is applied in the TDD system are limited to DL subframes thattransmit UL ACK/NACK for the same UL subframe in accordance with ULACK/NACK transmission rule of the 3GPP LTE).

TABLE 6 UL-DL Subframe n Configuration 0 1 2 3 4 5 6 7 8 9 0 0 0 0 0 10, 1 0 0 0, 1 0 0 2 0, 1, 2 0, 1 0 0, 1, 2, 3 0, 1, 2 0, 1 0 0, 1, 2, 33 0 0, 1, 2 0, 1 0 0, 1 0 0, 1 4 0, 1, 2, 3 0, 1, 2 0, 1 0 0, 1, 2, 3 0,1, 2 0, 1 0 5 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 4 0, 1, 2,3 0, 1, 2 0, 1 0 0, 1, 2, 3, 4, 5, 6, 7 4, 5, 6 4, 5 4, 5, 6, 7, 8 6 0 00 0 0

Multi-Subframe Scheduling Method in Carrier Aggregation Status

The method for performing multi-subframe scheduling in a single carrierstatus has been described as above. The aforementioned methods maysimilarly be applied to a multi-carrier status. The operation ofmulti-subframe scheduling in a carrier aggregation status becomes thescheduling operation of different subframes of different CCs for aspecific subframe of a specific CC in view of the base station. In otherwords, cross scheduling is performed for CC, subframe, andtwo-dimensional resources. Accordingly, a cross-scheduling indicator fortwo-dimensional resources will be required for the PDCCH that schedulesPDSCH/PUSCH.

First of all, a method for performing multi-subframe scheduling in acarrier aggregation status by using a resource indicator extended fromthe carrier indicator or subframe indicator will be described. In thismethod, the carrier indicator and the subframe indicator arejoint-encoded to one resource indicator (or resource indication field).Accordingly, both cross-scheduling and multi-subframe scheduling may beperformed using one resource indicator. To this end, the base stationmay semi-statically set the number N_(R) of bits of the resourceindicator through an higher layer (for example, RRC) signal and notify aspecific user equipment of the number N_(CC) of CCs, which areconfigured. Since the number of total states of the resource indicatorexpressed as N_(R) bits is 2̂(N_(R)), if the number of total states isgreater than N_(CC), the remaining state may be used for subframeindication. In more detail, if the total states are indexed as 0, 1, . .. , 2̂(N_(R))−1, states 0, 1, . . . , N_(CC)−1 may respectively beinterpreted as scheduling for CC 0, 1, . . . , N_(CC)−1 at m=0, andstates N_(CC), N_(CC)+1, . . . , 2N_(CC)−1 may respectively beinterpreted as scheduling for CC 0, 1, . . . , N_(CC)−1 at m=1. Thisinterpretation operation may be performed repeatedly, wherebymulti-subframe scheduling may be performed to reachm=floor{2̂(N_(R))}/N_(CC)≦−1. In this case, floor{x} means a maximuminteger smaller than or equal to x.

FIG. 14 is a diagram illustrating a multi-subframe scheduling method ina multi-carrier status. In more detail, FIG. 14 illustrates a subframeof CC scheduled by each state of a resource indicator (or resourceindication field) if N_(R)=3 and N_(CC)=3.

Referring to FIG. 14, the resource indicator includes three bits(N_(R)=3), it may indicate a total of eight states. Since the number ofCCs which are configured is 3 (N_(CC)=3), five remaining states may beused for multi-subframe scheduling. For example, as shown, states 0, 1,2 may be interpreted as scheduling for CC 0, 1, 2 at m=0, and states 3,4, 5 may be interpreted as scheduling for CC 0, 1, 2 at m=1.Multi-subframe scheduling (for example, m=2) for all the three CCscannot be performed by states 6 and 7, and the states 6 and 7 arereserved in the drawing. However, unlike FIG. 14, the states 6 and 7 maybe used as scheduling indicators corresponding to m=2 at CC0 and CC1,respectively.

As another method, in a state that the carrier indicator and thesubframe indicator may exist independently, resource allocation formulti-subframe scheduling may be performed.

FIG. 15 is a diagram illustrating a base station and a user equipment,which may be applied to one embodiment of the present invention. If arelay is included in a wireless communication system, communication in abackhaul link is performed between the base station and the relay andcommunication in an access link is performed between the relay and theuser equipment. Accordingly, the base station or the user equipment asshown may be replaced with the relay depending on the circumstances.

Referring to FIG. 15, the wireless communication system includes a basestation (BS) 110 and a user equipment (UE) 120. The base station 110includes a processor 112, a memory 114, and a radio frequency (RF) unit116. The processor 112 may be configured to implement procedures and/ormethods suggested in the present invention. The memory 114 is connectedwith the processor 112 and stores various kinds of information relatedto the operation of the processor 112. The RF unit 116 is connected withthe processor 112 and transmits and/or receives a radio signal. The userequipment 120 includes a processor 122, a memory 124, and a radiofrequency (RF) unit 126. The processor 122 may be configured toimplement procedures and/or methods suggested in the present invention.The memory 124 is connected with the processor 122 and stores variouskinds of information related to the operation of the processor 122. TheRF unit 126 is connected with the processor 122 and transmits and/orreceives a radio signal. The base station 110 and/or the user equipment120 may have a single antenna or multiple antennas.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predetermined type.Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention. The order of operations described in theembodiments of the present invention may be changed. Some structuralelements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment. Moreover, it will be apparent that someclaims referring to specific claims may be combined with another claimsreferring to the other claims other than the specific claims toconstitute the embodiment or add new claims by means of amendment afterthe application is filed.

The embodiments of the present invention have been described based onthe data transmission and reception between the base station and theuser equipment. A specific operation which has been described as beingperformed by the base station may be performed by an upper node of thebase station as the case may be. In other words, it will be apparentthat various operations performed for communication with the userequipment in the network which includes a plurality of network nodesalong with the base station may be performed by the base station ornetwork nodes other than the base station. The base station may bereplaced with terms such as a fixed station, Node B, eNode B (eNB), andaccess point. Also, the user equipment may be replaced with terms suchas mobile station (MS) and mobile subscriber station (MSS).

The embodiments according to the present invention may be implemented byvarious means, for example, hardware, firmware, software, or theircombination. If the embodiment according to the present invention isimplemented by hardware, the embodiment of the present invention may beimplemented by one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, microcontrollers,microprocessors, etc.

If the embodiment according to the present invention is implemented byfirmware or software, the embodiment of the present invention may beimplemented by a type of a module, a procedure, or a function, whichperforms functions or operations described as above. A software code maybe stored in a memory unit and then may be driven by a processor. Thememory unit may be located inside or outside the processor to transmitand receive data to and from the processor through various means whichare well known.

It will be apparent to those skilled in the art that the presentinvention may be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

INDUSTRIAL APPLICABILITY

The present invention may be used for a wireless communication devicesuch as a user equipment, a relay and a base station.

1. A method for receiving a downlink signal in a user equipment of awireless communication system, the method comprising the steps of:receiving a physical downlink control channel (PDCCH) signal, whichincludes scheduling information, from a base station on a firstsubframe; receiving a physical downlink shared channel (PDSCH) signalcorresponding to the PDCCH signal, from the base station on a secondsubframe; and decoding the PDSCH signal, wherein an interval between thefirst subframe and the second subframe is varied.
 2. The methodaccording to claim 1, wherein the interval between the first subframeand the second subframe is varied by predetermined information withinthe PDCCH signal.
 3. The method according to claim 1, wherein theinterval between the first subframe and the second subframe is varied byconsidering at least one of carrier configuration for the user equipmentand a value of a carrier indication field within the PDCCH signal. 4.The method according to claim 3, wherein, if a single carrier isconfigured for the user equipment, the value of the carrier indicationfield is used to indicate the second subframe, if a multi-carrier isconfigured for the user equipment, the value of the carrier indicationfield is used to indicate a carrier to which the PDSCH signal istransmitted, and the first subframe and the second subframe are givenequally.
 5. The method according to claim 3, wherein, if a singlecarrier is configured for the user equipment, the value of the carrierindication field is used to indicate the second subframe, and if amulti-carrier is configured for the user equipment, the value of thecarrier indication field is used to indicate combination of the carrierto which the PDSCH signal is transmitted and the second subframe.
 6. Themethod according to claim 1, further comprising the step of transmittinga physical uplink control channel (PUCCH) signal, which includesreception acknowledgement information for the PDSCH signal, on a thirdsubframe, wherein a resource for the PUCCH signal is inferred from aresource used to transmit the PDCCH signal, and an index of the thirdsubframe is inferred from that of the second subframe used to transmitthe PDSCH signal.
 7. The method according to claim 1, further comprisingthe step of transmitting a PUCCH signal, which includes receptionacknowledgement information for the PDSCH signal, on a third subframe,wherein transmission of the PUCCH signal is dropped on the thirdsubframe if an interval between the second subframe and the thirdsubframe is smaller than a predetermined value.
 8. A user equipment foruse in a wireless communication system, the user equipment comprising: aradio frequency (RF) unit; and a processor, wherein the processor isconfigured to receive a physical downlink control channel (PDCCH)signal, which includes scheduling information, from a base station on afirst subframe, receive a physical downlink shared channel (PDSCH)signal corresponding to the PDCCH signal from the base station on asecond subframe, and decode the PDSCH signal, and an interval betweenthe first subframe and the second subframe is varied.
 9. The userequipment according to claim 8, wherein the interval between the firstsubframe and the second subframe is varied by predetermined informationwithin the PDCCH signal.
 10. The user equipment according to claim 8,wherein the interval between the first subframe and the second subframeis varied by considering at least one of carrier configuration for theuser equipment and a value of a carrier indication field within thePDCCH signal.
 11. The user equipment according to claim 10, wherein, ifa single carrier is configured for the user equipment, the value of thecarrier indication field is used to indicate the second subframe, if amulti-carrier is configured for the user equipment, the value of thecarrier indication field is used to indicate a carrier to which thePDSCH signal is transmitted, and the first subframe and the secondsubframe are given equally.
 12. The user equipment according to claim10, wherein, if a single carrier is configured for the user equipment,the value of the carrier indication field is used to indicate the secondsubframe, and if a multi-carrier is configured for the user equipment,the value of the carrier indication field is used to indicatecombination of the carrier to which the PDSCH signal is transmitted andthe second subframe.
 13. The user equipment according to claim 8,wherein the processor is further configured to transmit a physicaluplink control channel (PUCCH) signal, which includes receptionacknowledgement information for the PDSCH signal, on a third subframe, aresource for the PUCCH signal is inferred from a resource used totransmit the PDCCH signal, and an index of the third subframe isinferred from that of the second subframe used to transmit the PDSCHsignal.
 14. The user equipment according to claim 8, wherein theprocessor is further configured to transmit a PUCCH signal, whichincludes reception acknowledgement information for the PDSCH signal, ona third subframe, and transmission of the PUCCH signal is dropped on thethird subframe if an interval between the second subframe and the thirdsubframe is smaller than a predetermined value.